Conventionally, a brazing sheet is used for brazing aluminum-containing members. As a brazing sheet, clad metal produced by joining brazing filler metal such as a 4343 alloy (hereinafter, four characters consisting of digits or of digits and a letter (or letters) indicate those defined by JIS) and a 4045 alloy on one side or both sides of a core material such as a 3003 alloy and a 3N03 alloy is used. When brazing is conducted by using such a brazing sheet, the brazing filler metal is joined also on portions other than portions which should be brazed. This causes a manufacturing cost of an end product to be increased. In addition, there is a limit to a thickness due to manufacturing reasons, so that clad metal used as the brazing sheet has to have a thickness of at least approximately 60 μm. It is extremely difficult to manufacture clad metal having a thickness thinner than the above-mentioned thickness due to industrial reasons. Even if the clad metal having the thickness thinner than the above-mentioned thickness can be manufactured, a thickness of a skin material is not uniform, thereby failing to attain stable quality and properties.
In recent years, there has been proposed a method in which without using the brazing sheet, brazing is conducted by coating a mixture of an aluminum-silicon-based brazing filler metal powder and flux on portions of aluminum-containing members, which are to be brazed.
In Japanese Patent Application Laid-Open Publication No. 2003-334690 (Patent Document 1), aluminum alloy powder brazing filler metal which contains 4 to 13% by mass of Si and 0.5 to 20% by mass of Zn, whose remainder includes Al and an impurity, and which has an average particle diameter of 1 to 100 μm is described.
In Japanese Patent Application Laid-Open Publication No. 10-323792 (Patent Document 2), an aluminum alloy powder brazing filler metal comprising: a powder obtained by mixing an Al—Si—Zn ternary hypereutectic alloy powder which contains 13 to 45% of Si and 6 to 35% of Zn, whose remainder has composition of Al and an enevitable impurity, and which has an average particle diameter is 5 to 100 μm; and an Si powder which has an average particle diameter of 5 to 50 μm is described.
Further, in Japanese Patent Application Laid-Open Publication No. 2001-293593 (Patent Document 3), a pasty composition for aluminum brazing obtained by mixing a pure aluminum powder whose brazing metal powder has an average particle diameter of greater than or equal to 1 μm and less than 10 μm and a silicon power which has an average particle diameter of greater than or equal to 0.1 μm and less than 10 μm is described. When these conventional brazing filler metal powders for aluminum brazing are used, there have accrued problems that dimensional accuracy of products obtained after the brazing are still insufficient and that erosion (a deterioration in a surface roughness) is caused.
Patent Document 1: Japanese Patent Application Laid-Open Publication No. 2003-334690
Patent Document 2: Japanese Patent Application Laid-Open Publication No. 10-323792
Patent Document 3: Japanese Patent Application Laid-Open Publication No. 2001-293593